Laboratory mice are by far the most used animals in biomedical research globally, yet their welfare receives less attention than larger species. The 3Rs framework — Replace, Reduce, Refine — provides the foundation for improving mouse welfare at scale.
Mouse welfare in research is compromised by institutional inertia, assumption of low sentience based on size, and outdated husbandry standards. Single housing causes acute and chronic stress; yet it persists in many facilities despite evidence that group housing does not compromise most research. Barren standard cages prevent nesting, burrowing, and climbing — behaviors mice are strongly motivated to perform. Genetically modified lines with pathological phenotypes (spontaneous cancer, immune deficiency, neurological disease) require welfare assessments throughout their lives but often receive inadequate monitoring. Refinement — improving the welfare of animals that must be used — offers the largest near-term impact, as full replacement of mouse models remains distant for most research applications.